There are two main conventional approaches to pumping liquid from a deep well. One, the pump is placed in the bottom of the well, or, two, the main body of the pump is at the surface and a long shaft drives a pump mechanism at the bottom of the well. Both approaches have shortcomings, especially for very deep wells. The first method is generally restricted to very small pumps that can only pump a very limited height and the second method, such as used in oil wells, involves moving large masses of connecting rods, which requires huge and costly equipment and results in inefficiencies.
Many conventional pumps use a bottom piston located close to the liquid intake. The piston moving up and down affects the liquid level in the well and agitates sand and other abrasive materials that are then more likely to enter and damage the pump.